it is a taxing event anyway. they have got medical personnel right there at scene because so many runners are just absolutely maxed out when they cross the finish line. >> exactly. as we do here in new york city, we have medical tents set up, a lot of them at the finish line. it was great the doctors and first-responders were there to help administer care. the problem is they're not set up for an explosion or disaster of this sort but definitely helps to have the medical care present. jon: you say one of the things people should be alert for in the weeks and months, years to come is ptsd, posttraumaic stress disorder. >> yes. after a event like this which is horrific in nature, it also stirs deep emotions in lots of people. people will become depressed and many will suffer recurrent nightmares and visions of this type of trauma if they were actually there and witnessed it. we have to be alert for that occurring in both adults and children. anybody who was witness to this is subject to that it is something we have